Large-diameter sic wafer and manufacturing method thereof

ABSTRACT

From the viewpoint of manufacturing an SiC semiconductor device economically, a present Si device manufacturing line is utilized to make it possible to handle a small-diameter SiC wafer. Polycrystal SiC is grown from at least one surface side of a small-diameter a-SiC single crystal wafer so as to be in a size of an outer diameter corresponding to a handling device of an existing semiconductor manufacturing line, and thereafter the polycrystal SiC on the surface of the α-SiC single crystal wafer is ground to manufacture an increased-diameter SiC of a double structure in which the polycrystal SiC is grown around an outer circumference of the small-diameter α-SiC single crystal wafer.

TECHNICAL FIELD

This invention relates to a large-diameter SiC wafer and a manufacturingmethod thereof, and particularly relates to an SiC wafer increased inits diameter so that an SiC single crystal wafer used in an SiCsemiconductor manufacturing process is made available for practical use,and a manufacturing method thereof.

BACKGROUND ART

There is a liquid phase lifting method in which a seed crystal, which isa base of crystal growth, is immersed in molten silicon while beingrotated and is then gradually lifted, on producing an ingot of Si.However, since SiC does not have liquid phase below 3000° C., thereforea sublimation recrystallization method is widely adopted. However, amanufacturing technique of the SiC wafers is not matured, and many ofwafers that can be manufactured contain crystal defects in crystal.Since crystal of good quality is not obtained in large-diameter wafers,the size of α-SiC single crystal wafer for SiC semiconductors and GaNemission laser, which is made available for practical use, is limited toabout two inches, though it is sold on the market.

On the other hand, as for a device, which can handle an ordinary siliconsingle crystal wafer, there exist the ones which handle the wafers of 6inches to 12 inches, and no semiconductor manufacturing line can handleα-SiC single crystal wafers of the size of two inches, which are smallerthan the above wafers. This makes it possible to manufacture SiC wafersin the size of two inches available for practical use, but they cannotbe provided to the actual industrial world. There is an increased demandespecially for putting α-SiC single crystal wafers into practical use,because the α-SiC single crystal wafer has high dielectric strength.Consequently, it is desired to handle this in the semiconductormanufacturing line.

As the above-described manufacturing method of large-diameter siliconsingle crystal wafers, Japanese Patent Laid-open No. 10-55975 is known.This manufacturing method is for growing polycrystal or single crystalSi around an Si single crystal rod. However, since the silicon singlecrystal rod is used for a raw material, the device becomes large-scaled,and the raw material applied to this method is only Si, but SiC that isa promising semiconductor material is not disclosed. Further, theobtained double ring layer structure Si is about 1.1 times as large asthe raw material diameter and it is difficult to call it achievement ofa large diameter.

Paying attention to the above-described problem of the prior art, fromthe viewpoint of economically manufacturing the SiC semiconductordevices, the present invention has its object to provide alarge-diameter SiC wafer, which utilizes the present Si devicemanufacturing line to make it possible to handle the SiC wafers, and themanufacturing method thereof.

DISCLOSURE OF THE INVENTION

The present invention is to grow a polycrystal SiC with an outerdiameter of six inches and an inner diameter of two inches around, forexample, an α-SiC single crystal wafer of two inches generally sold onthe market. This is obtained by the knowledge that manufacturing of anSiC device by utilizing an existing Si manufacturing line of four inchesor more becomes possible due to the above.

Namely, the present invention is characterized by increasing in thediameter as a double structure in which a polycrystal SiC is grown to bein a size, which corresponds to a handling device of the existingsemiconductor manufacturing line, around an outer circumference of asmall-diameter α-SiC single crystal wafer. In this case, it is desirableto place at least two or more of the aforementioned small-diameter α-SiCsingle crystal wafers. It is also desirable to make the aforesaidpolycrystal SiC to be β-SiC manufactured by a CVD method. Further, it issuitable to constitute the aforesaid polycrystal SiC to have highreflectivity with respect to the laser light for wafer detection.

A manufacturing method of a large-diameter SiC wafer according to thepresent invention is characterized by including the steps of growingpolycrystal SiC from at least one surface side of a small-diameter α-SiCsingle crystal wafer so as to have an outer diameter size correspondingto a handling device of an existing semiconductor manufacturing line,and thereafter grinding the polycrystal SiC on a surface of the α-SiCsingle crystal wafer to manufacture an increased-diameter SiC of adouble structure in which the polycrystal SiC is grown around an outercircumference of the small-diameter α-SiC single crystal wafer.

According to the above-described constitution, a structure of the waferin which a polycrystal SiC is formed at a peripheral portion of theα-SiC single crystal wafer is provided. This makes it possible to usethe apparatus for the existing Si device to manufacture the SiC device.Since α-SiC is used in the manufacturing line of the Si device, theα-SiC transmits the laser light due to a large band gap with respect tothe laser light of the wafer detecting device, and it is determined thatthe wafer does not exist, even when the wafer actually exists. However,by placing the polycrystal SiC having high reflectivity with respect tothe laser light around the α-SiC, wafer detection is made possible inthe existing device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a large-diameter SiC wafer according to anembodiment of the present invention;

FIG. 2 is a sectional side view of an α-SiC wafer manufacturingapparatus according to the embodiment of the present invention;

FIG. 3 is a sectional side view of a manufactured SiC wafer according tothe embodiment of the present invention; and

FIG. 4 is a sectional side view of a manufactured α-SiC wafer accordingto the embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of a large-diameter SiC wafer according to the presentinvention and a manufacturing method thereof will be explained in detailwith reference to the drawings.

A preferred embodiment of an SiC wafer according to the embodiment willbe explained with a wafer of six inches taken as an example.

First, an α-SiC wafer 10 being a material of the large-diameter SiCwafer may be manufactured as follows, for example. FIG. 2 is a sectionalside view of an α-SiC wafer manufacturing apparatus 1. In FIG. 2, agraphite crucible 11 is placed in a center part. The graphite crucible11 is formed by a crucible body 13 and a lid 15. An SiC raw material 17is housed in a lower part inside the crucible body 13, and an α-SiCsubstrate 19 is attached to the lid 15.

The graphite crucible 11 has its outer circumference surrounded by aheat insulation material 21, and is set in a high-frequency furnace notshown. The high-frequency furnace has, for example, a high-frequencycoil 23 set on its outer side and has a hollow duplex tube 25 made ofquartz constituted of dual tubes made of a quartz material inside it.Cooling water 27 flows between the duplex tubes of the duplex tube 25made of quartz. The high-frequency furnace is controlled at a fixedtemperature by an output produced from a high-frequency oscillator notshown. Consequently, a surface of the graphite crucible 11 is measuredwith a pyrometer 29 from a clearance of a heat insulating material 21 atits upper portion and lower portion, and the graphite crucible 11 iskept at a fixed temperature by the high-frequency coil 23 beingcontrolled by the output produced by the high-frequency oscillator. Whenthe high-frequency furnace is heated, the SiC material 17 and the α-SiCsubstrate 19 inside the graphite crucible 11 are heated to about 2,200°C. to 2,400° C. An α-SiC phase 31 is deposited on a surface of the α-SiCsubstrate 19 and an SiC 33 is formed.

Consequently, as shown in FIG. 3, the α-SiC phase 31 of 6H crystal ofthickness of Ta=10˜50 mm grows on the α-SiC substrate 19, and by usingsingle crystal for the substrate, single crystal of the same size asthat of the substrate diameter can be obtained. Then, the obtainedsimple crystal bulk (10˜50 mm) was at and polished, whereby an α-SiCwafer 50 of 6H is obtained as shown in FIG. 4.

The α-SiC wafer 50 of two inches with the thickness of 0.5 mmmanufactured according to the sublimation recrystallization method asdescribed above is used in this embodiment.

FIG. 1 shows a manufacturing process of the large-diameter α-SiC wafer.As shown in FIG. 1 (1), the α-SiC wafer 50 is set at a center part of agraphite circular plate 52 with the diameter of 6 inches. Further, agraphite masking 54 is placed on the α-SiC wafer 50.

In this state, a chemical vapor deposition (CVD) method is carried outfrom the direction of the arrows onto the graphite circular plate 52 andthe masking 54 as shown in FIG. 1(2). Namely, SiH₄, SiHCl₃ and the likeare used as a source of Si, and C₃H₈ and the like are used as a sourceof C for the α-SiC single crystal wafer on the graphite plate and theyare supplied to a CVD reactor, and inside the CVD reactor, SiC ischemically deposited on the graphite plate and the single crystal wafer.The size of a polycristalline substance formed on the α-SiC singlecrystal wafer is determined according to the size of graphite plate.According to this, polycrystal a β-SiC 56 with the thickness of 0.8 mmis grown. This process is carried out under the temperature condition ofless than 2000° C. to grow the β-SiC 56.

After the chemical vapor deposition, the surplus β-SiC 56 is removed bybeing ground until a surface of the masking 54 is exposed (FIG. 1(3)).The graphite circular plate 52 and the masking 54 are burnt down, andthus a large-diameter SiC 60 having a double structure of concentriccircles can be obtained.

A grinding work and a polishing work are performed for thelarge-diameter SiC 60, and as shown in FIG. 1(4), a six-inchlarge-diameter SiC 60 of single plate constituted of a wafer centerportion being a single crystal α-SiC wafer 50 two inches in size and aperiphery portion being a polycrystal β-SiC 56 is obtained. The singlecrystal α-SiC wafer 50 at the center portion of the obtainedlarge-diameter SiC 60 is colorless and transparent, or green andtransparent, and the polycrystal β-SiC 56 of the periphery portion isyellow or black. Since the obtained large-diameter SiC 60 has thepolycrystal β-SiC 56 having high reflectivity with respect to laserlight placed at the periphery portion, it is detectable with respect tothe laser light of a wafer detection device used in the Si devicemanufacturing line.

In the above-described embodiment, the polycrystal SiC is formed at theperiphery portion, but it does not always have to be a β phase. It doesnot always have to be produced by the CVD method, and a sublimationmethod may be used other than this. When SiC is used for the peripheryportion in this sublimation method, it is allowed to react at a hightemperature, and therefore the crystal system becomes α-SiC of a stablelayer.

The handling device of the existing Si semiconductor line can be used asit is for the large-diameter SiC 60 thus constituted. Due to this, adevice can be formed in the area of the α-SiC wafer 50 two inches insize, and the α-SiC wafer 50 can be made available for practical use.Accordingly, it becomes possible to use the α-SiC wafer 50 at apractical level, which can be only applied to the semiconductor devicein a range of a laboratory facility, and it can be used in thesemiconductor industry.

In the above-described embodiment, the α-SiC wafer 50 is placed at thecenter portion of the large-diameter SiC 60. However, the α-SiC wafer 50may be formed at a position displaced from the center. Alternatively, itis possible to place a plurality of two-inch α-SiC wafers 50 in a planeof the large-diameter graphite circular plate 52. This is made possiblesince the technique of depositing the β-SiC 56 on the α-SiC wafer 50placed on the graphite circular plate 52 is used as shown in FIG. 1.

As explained thus far, the present invention adopts the constitution ofthe increased diameter as a double structure in which the polycrystalSiC is grown to be in the size, which corresponds to the handling deviceof the existing semiconductor manufacturing line, in the outercircumference of the small-diameter α-SiC single crystal wafer.Accordingly, from the viewpoint of economically manufacturing the SiCsemiconductor device, the effects of making it possible to handle theSiC wafer by utilizing the present Si device manufacturing line can beobtained.

INDUSTRIAL AVAILABILITY

The SiC semiconductor manufacturing method according to the presentinvention increases the diameter of the α-SiC single crystal wafer twoinches in size and makes it possible to utilize it in the handlingdevice of the existing semiconductor manufacturing line.

1. A large-diameter SiC wafer, wherein a diameter is increased as adouble structure in which a polycrystal SiC is grown up to be in a size,which corresponds to a handling device of an existing semiconductormanufacturing line, around an outer circumference of a small diameterα-SiC single crystal wafer.
 2. The large-diameter SiC wafer according toclaim 1, wherein at least two or more of said small-diameter α-SiCsingle crystal wafers are placed.
 3. The large-diameter SiC waferaccording to claim 1, wherein said polycrystal SiC is a β-SiCmanufactured by a CVD method.
 4. The large-diameter SiC wafer accordingto claim 1, wherein said polycrystal SiC has high reflectivity withrespect to laser light for wafer detection.
 5. A manufacturing method ofa large-diameter SiC wafer comprising the steps of: growing polycrystalSiC from at least one surface side of a small diameter α-SiC singlecrystal wafer so as to be in a size of an outer diameter correspondingto a handling device of an existing semiconductor manufacturing line;and thereafter grinding the polycrystal SiC on the surface of the α-SiCsingle crystal wafer to manufacture an increased-diameter SiC of adouble structure in which the polycrystal SiC is grown around an outercircumference of the small-diameter α-SiC single crystal wafer.